linux-ext4 - Re: [v10 4/5] ext4: adds FS_IOC_FSSETXATTR/FS_IOC

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Message-ID: <CAPTn0cBk8MEFxZRyuUg-D6=sSb+0eYcHWRtji-xUPYgCyBsRrA@mail.gmail.com>
Date:	Wed, 1 Apr 2015 17:00:01 +0800
From:	Li Xi <pkuelelixi@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	"Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger@...ger.ca>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"hch@...radead.org" <hch@...radead.org>,
	Dmitry Monakhov <dmonakhov@...nvz.org>
Subject: Re: [v10 4/5] ext4: adds FS_IOC_FSSETXATTR/FS_IOC_FSGETXATTR
 interface support

Hi Jan Kara,

Hope you‘ve recovered physically. :)

I've pushed the version 11 patches which still disallow the ownder of
a file to change its project ID. I will remove this limit in the
coming verion 12 patches.

On Wed, Apr 1, 2015 at 3:20 PM, Jan Kara <jack@...e.cz> wrote:
> On Fri 20-03-15 21:24:07, Li Xi wrote:
>> On Thu, Mar 19, 2015 at 5:56 PM, Jan Kara <jack@...e.cz> wrote:
>> > On Thu 19-03-15 04:04:56, Li Xi wrote:
>> >> This patch adds FS_IOC_FSSETXATTR/FS_IOC_FSGETXATTR ioctl interface
>> >> support for ext4. The interface is kept consistent with
>> >> XFS_IOC_FSGETXATTR/XFS_IOC_FSGETXATTR.
>> >   Two more comments below.
>> >
>> >>
>> >> Signed-off-by: Li Xi <lixi@....com>
>> > ...
>> >> +static int ext4_ioctl_setproject(struct file *filp, __u32 projid)
>> >> +{
>> >> +     struct inode *inode = file_inode(filp);
>> >> +     struct super_block *sb = inode->i_sb;
>> >> +     struct ext4_inode_info *ei = EXT4_I(inode);
>> >> +     int err;
>> >> +     handle_t *handle;
>> >> +     kprojid_t kprojid;
>> >> +     struct ext4_iloc iloc;
>> >> +     struct ext4_inode *raw_inode;
>> >> +
>> >> +     struct dquot *transfer_to[EXT4_MAXQUOTAS] = { };
>> >> +
>> >> +     /* Make sure caller can change project. */
>> >> +     if (!capable(CAP_SYS_ADMIN))
>> >> +             return -EACCES;
>> >   Why do you test capabilities here when you already test permission in
>> > EXT4_IOC_FSSETXATTR? Furthermore this test is too restrictive. Just delete
>> > it.
>> It seems we need this restrictive permission. Otherwise the owner of the file
>> can change the project ID to any other project. That means, the owner can
>> walk around the quota limit whenever he/she wants. But I agree checking
>> permission twice is not good.
>   Sorry for a late reply but I was catching up with stuff after a
> conference and then got ill. So I agree that owner of a file can escape
> project quota limit whenever he/she wants by setting project to something
> else. Sadly that's how project quota has been originally designed and how
> it works in XFS for years. So we should start with being compatible with
> this behavior.
>
> Konstantin has in his patches patch "fs: protected project id" which
> creates a sysctl which controls whether or not owner is able to set
> arbitrary project id. That is one way to improve the situation so that
> project quotas are usable also in situations where setting project quotas
> to any project by file owner is undesirable. Christoph also had an idea
> that we could allow owner to set project to anything when current project
> is unset (0). Once project is set, only CAP_SYS_ADMIN (maybe better
> capability would be CAP_CHOWN actually) process can change it. We can
> discuss how to change the current XFS model to suit new usecases but IMHO
> we should start the way XFS is...
>
>                                                                 Honza
> --
> Jan Kara <jack@...e.cz>
> SUSE Labs, CR
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